1. Field of the Invention
The present invention relates to a structured-light pattern, and more particularly, to a method for generating a structured-light pattern. Although the present invention is suitable for a wide scope of applications, it is particularly suitable for using a single frame or two frames, thereby obtaining high-resolution real-time three-dimensional (3D) data.
2. Discussion of the Related Art
Triangulation-based structured-lighting in one of the most widely used methods of active range sensing and various approaches have been suggested and tested. Recently, interests have been developed in rapid range sensing of moving objects, such as cloth, human face and body in one or slightly more video frames, and much attention has been paid to the use of color to increase the number of distinguishable patterns in an effort to decrease the number of structured-light projections required for ranging a scene. Hereinafter, the design of stripe patterns and the selection of colors to assign to stripe illumination patterns that minimize the effects of object surface colors, system noise, nonlinearity and limitations in camera/projector resolution for real-time range imaging in a single video frame (also referred to as “one-shot”) and for near real-time imaging in double video frames (also referred to as “two-shot”) will be described.
Among the systems adopting a single illumination source (or projector) and a single camera, as shown in FIG. 1, the systems that project sweeping laser light plane, black-and-white (BW) stripe patterns, gray-level stripes have been well investigated. (See refs.: M. Rioux, G. Bechthold, D. Taylor, and M. Duggan, “Design of a large depth of view three-dimensional camera for robot vision,” Optical Engineering, 26(12):12451250, December 1987., K. Sato and S. Inokuchi, “Three-dimensional surface measurement by space encoding range imaging,” Journal of Robotic System, 2:2739, 1985., and E. Horn and N. Kiryati, “Toward optical structured-light patterns,” Image and Vision Computing, 17, 1999.) Since such systems project multiple light patterns or sweeping laser stripe, the systems are appropriate for stationary scenes. Hall-Holt and Rusinkiewicz have recently suggested a method based on time-varying binary BW patterns for near real-time ranging in four video frames. However, object motion is assumed to be slow to keep “time coherence”, which is disclosed in detail by O. Hall-Holt and S. Rusinkiewicz, “Stripe boundary codes for real-time structured-light range scanning of moving objects,” Proc. ICCV, 2001.
Various approaches have been made to one-shot or near one-shot imaging. One class of methods is those that project continuous light patterns: Tajima and Iwakawa used rainbow pattern with continuous change of light color (See ref:: J. Tajima and M. Iwakawa, “3-D data acquisition by rainbow range finder,” Proc. 10th ICPR, pp. 309-313, Atlantic City, N.J., 1990.), Huang et al. used sinusoidal color fringe light with continuous variation of phase (See ref.: P.S. Huang, Q. Hu, F. Jin, and F. Chiang, “Color-encoded digital fringe projection technique for high-speed three-dimensional surface contouring,” SPIE Optical Engineering, Vol. 38(06), pp. 1065-1071, 1999.), and Carrihill and Humel used gray-level ramp and constant illumination (See ref.: B. Carrihill and R. Humel, “Experiments with the intensity ratio depth sensor,” Computer Vision, Graphics, and Image Processing, 32:337358, 1985.). Although all of the above-described methods can principally produce range images with high speed and high resolution only restricted by system resolution, they are highly susceptible to system noise, nonlinearlity, and object surface colors. Another class of approaches includes those that use discrete color patterns: Davies and Nixon designed a color-dot illumination pattern, Boyer and Kak developed color stripe patterns that can be identified by a color coding of adjacent stripes, and Zhang et al. also develoed a color stripe pattern based on a de Bruijn sequence and stripes are identified by dynamic programming. (See refs.: C. J. Davies and M. S. Nixon, “A hough transformation for detecting the location and orientation of three-dimensional surfaces via color encoded spots,” IEEE Trans. On Systems, Man, and Cybernetics, 28(1B), 1998., K. L. Boyer and A. C. Kak, “Color-encoded structured-light for rapid active ranging,” IEEE Transactions on Pattern Analysis and Machine Intelligence 9, No. 1, 14-28, 1987., and L. Zhang, B. Curless, S. M. Seitz, “Rapid shape acquisition using color structured-light and multi-pass dynamic programming,” 1st International Symposium on 3D Data processing, Visualization, and Transmission, Padova, Italy, Jun. 19-21, 2002.)
Although the color-dot and color-stripe methods are less sensitive to system noise and nonlinearity as compared to those with continuous light patterns, the color-dot and color-stripe methods are also significantly affected by object color reflectance, and their range resolution is limited by stripe width. Caspi et al. presented a three-image-frame method that can overcome the ambiguity in stripe labeling due to object surface color, but its real-time application has not been explicitly considered. (See ref.: D. Caspi, N. Kiryati and J. Shamir, “Range imaging with adaptive color structured-light,” IEEE PAMI, Vol. 20, pp. 470-480, 1998.)
Most of the color stripe-based methods suggest design of color patterns that can be uniquely identified in the illumination space, but little explicit attention has been paid to the selection of colors. In this description, we investigate the selection of colors for illumination stripe patterns for maximizing range resolution, and present novel one-shot (single frame) and two-shot (double) imaging methods, which is insensitive to system noise, nonlinearity, object color reflectance, and ambient lights.